Radial piston machines, this means radial piston pumps and radial piston engines, among other things can be differentiated in how hydraulic fluid is provided to operating cavities in the radial cylinder block. It is known from EP-A-0 401 408 that the supply and removal of hydraulic fluid is performed through a stationary control pinion that is connected with the housing. Disadvantages of this very widely used configuration are that only rather narrow flow channels (inlet and outlet channels) can be implemented in the control pinion and that due to the flow channels axially run out of the control pinion, the mechanical bending load on the control pinion is rather high. It can be recited as an advantage of the known configuration that the bearing of an input- or output shaft is hardly loaded. However, the fit between the outer enveloping surface of the control pinion and the inner enveloping surface of the rotating radial cylinder block is rather problematic. Therein due to the configuration no zero gap is feasible, wherein the leakage increases with the third power of the clearance, which yields greater leakage rates in particular for increasing wear. Furthermore the known principle of control pinion radial cylinder block fit is sensitive to hydraulic fluids contaminated with dirt particular and sensitive to rapid temperature changes.
An alternative principle of supplying/removing hydraulic fluid to/from the radial cylinder block is known from the printed documents DE-A-1 812 635, DE-A-24 52 092, DE-A-41 23 674, and DE-A-41 23 675. In the configuration disclosed in these printed documents the control plate element which can also be integrally configured in one piece with the housing is arranged axially adjacent to the radial cylinder block. Problems of this configuration are large axial forces and the need to support these large axial forces in a permanent manner with little wear. Furthermore the radial reactive forces from the hydraulic pressure impact the shaft and have to be received by the shaft bearings.
A radial piston machine as described supra is known e.g. from U.S. Pat. No. 3,951,044. The machine disclosed therein includes two control plate bodies arranged on opposite sides of the radial cylinder block, wherein the control plate bodies have a spherical configuration on each side oriented towards the radial cylinder block which spherical shape interacts with a hollow spherical shape of the lateral surfaces of the radial cylinder block arranged opposite thereto (c.f. in particular FIG. 4 provided therein). In order to prevent binding and friction between the control plate elements and the radial cylinder block during operation of the machine at least one control plate element is radially moveable in all directions in the known machine, this means in axial and also in radial direction. Consequently the rotating shaft connected with the radial cylinder block has to receive the radial forces generated during operation due to the hydraulic pressures. This in turn leads to an increased complexity for the shaft and its support and to potential wear.
The same principle of preventing possible alignment errors in the fit between the radial cylinder block and the control plate element(s) through the option of a radial displacement of at least one control plate element is also used as a basis for the machines according to DE-17776 238 A and U.S. Pat. No. 3,122,104 A. In the double stroke machine (two piston strokes per revolution) according to U.S. Pat. No. 3,122,104 A which does not include an eccentrical cam ring but an elliptical cam ring, this does not cause any problem due to the symmetry of the mutually balancing radial forces. In the single stroke machines with eccentric lifting ring the known principle, however, leads to significant friction and significant requirements with respect to the shaft bearing. For these reasons the solutions according to the three older printed documents have not been used in practical applications.